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tornado chart

A plot representing the effect of invasion on resistivity measurements that have different depths of investigation. The plot assumes a step-profilemodel of invasion and determines true resistivity, flushed zone resistivity and diameter of invasion from ratios of deep-, medium- and shallow-resistivity measurements. Strictly speaking, when both resistive invasion and conductive invasion are plotted, the chart is called a butterfly chart. When only one is plotted, it is known as a tornado chart.